The present invention relates to a process for manufacturing a whisker preform to be used as a fibrous base in the manufacture of a whisker reinforced composite material by infiltrating or impregnating a whisker with a matrix material such as a metal, alloy or plastic.
Various types of whiskers consisting of single crystals of SiC, Si.sub.3 N.sub.4 or graphite have, as inherent properties, extremely high standards of strength, elastic modulus, heat resistance, and chemical stability. For this reason, whiskers have been long considered as promising reinforcing material of metals or plastics. In spite of this, whiskers have not actually been used as reinforcing materials of metals or plastics in a practical sense. The most important technical reason for this is the difficulty in obtaining a uniform dispersion of a whisker in a matrix material. More specifically, various types of whiskers have been prepared by high temperature reaction of raw materials. The resultant products have a structural form in which dense, short fibrous whiskers entangle each other in a random manner and cannot be easily disentangled. This has impaired the uniform dispersion of a whisker in a matrix material and has prevented the practical use of a whisker as a reinforcing material.
It has been found that a structural form of a whisker may be transformed into a sponge-like cake form having an extremely uniform pore structure, depending upon the selection of the reaction system. Based on this finding, a manufacturing technique of a SiC whisker reinforced composite material had been proposed (Japanese Patent Application No. 57-130293) wherein the sponge-like cake of the resultant whisker is used as a fibrous base and a matrix material is introduced into the fibrous base. However, with this technique, if the preparation conditions of the whisker are not controlled under strict restrictions, a uniform structural base cannot be formed and properties of the resultant composite material sometimes suffer local variations (due to segregation).